(y/3+y/4)÷2=y/x
(y/3+y/4)=2y/x 两边同乘以2
(1/3+1/4)=2/x 两边同除以Y,Y不等于0
1/3-1/x+1/4=1/x 两边同减去1/X
1/3-1/x=1/x-1/4 两边同减去1/4